Another quiet update on the PLoS ONE interface. They have introduced an interface for user ratings. The overall rating can be seen in the right bar (when reading a paper on the site) and expanded to show a dissection into 3 categories: insight, reliability and style.
A click pops up a voting screen:
The nice detail is that we can query rating data by DOI. (example). It is not really an API, but the info is there and it is easily parsable. The PLoS ONE managing director, Chris Surridge, mentioned in the PLoS Facebook page, a couple of days ago that this change would be up soon.